The invention relates to an autocorrelator for connection to a pulsed laser for generating a display signal which enables the laser to be tuned in real time (with reference to a display of the display signal) down to the order of one picosecond pulse width. The invention also encompasses a method of producing autocorrelation traces.
The prior art techniques for the tuning of a pulsed laser for very short pulse widths was difficult because of the lack of efficient instrumentation and methods for tuning the laser in real time, i.e., with simultaneous display of the traces for reference in making tuning adjustments.
A trial-and-error procedure was generally used for tuning a pulsed laser for operation with pulse widths in the range of one to 100 picosecond. The laser was connected to a strip chart recorder, and a three to five minute long delay in readout on the recorder was often required. Tuning adjustments to the laser were made after the strip recorder printout was analyzed. The procedure was then repeated until the strip recorder finally indicated the desired result.
U.S. Pat. No. 4,190,366 to Doyle discloses an interferometer having a moving refractive element in one arm for scanning. The moving refractive element is a glass wedge which presents a greater or lesser thickness of glass for a light beam to pass through. The Doyle patent interferometer has the refractive element in one arm only, and motion of the element is reciprocal linear. Both of those features differ from the present invention.
The autocorrelator system of the present invention does not use an interference effect, as does the Doyle interferometer, and the refractive element of the present invention is used as a variable pulse time delay rather than as a variable phase shift.
Other prior art interferometers have used the well known linear motion of a mirror in one of the two split beam paths.
An article entitled "Real-Time Intensity Autocorrelation Interferometers", by R. L. Fork and F. A. Beisser, published in Applied Optics, Vol. 17, No. 22, pp. 3534-35, Nov. 15, 1979, describes an autocorrelator for obtaining real time performance by varying the path length of one interferometer arm. The path length is varied at audio frequencies by an oscillating glass corner cube mounted on the armature of a shaker device. A display of the temporal shape of pulses of one picosecond and less is obtained by a phase-matched sum frequency generation in a KDP crystal. The apparatus described in the article provides for calibration of the real time display by using a stepping motor to adjust the path length by a known distance.